Memory card and method of producing same

ABSTRACT

The invention relates to a memory card and its method of manufacture. The memory card has a flexible composite substrate formed from a top film, a base film, and an adhesive layer deposited between and bonding together the base film and the top film. Preferably, the thickness of such composite substrate is between 8 and 12 mils. A layer of metal is adhered to the exposed surface of the top film. A circuit layer is provided to form at least one site on the memory card which is readable by an external reading device. A protective layer is provided to overlie and protect the circuit layer of the memory card.

FIELD OF THE INVENTION

This invention relates to memory cards of the type used as prepaid cardsfor dispensing goods and/or services, and to an improved method forproducing such cards.

BACKGROUND OF THE INVENTION

Prepaid memory cards which enable their owner to perform purchaseswithout the use of cash or tokens have become very popular. Typically,such cards have been used to obtain a variety of goods and/or services,as for example, in vending machines for beverages or food, inprepayment: of public transportation such as buses, trains or subways,or for use with public telephones or photocopy machines.

Typically, the memory cards are one of several types: magneticallyreadable cards, microcircuit cards, and contactless cards. Magneticallyreadable cards have a magnetic stripe located on the outer surface whereinformation, such as remaining value of the card, is stored. They havethe advantage of being relatively inexpensive, and have been usedsuccessfully, for example, as fare cards for transit systems. However,this type of card is of limited usefulness as a prepaid card forsecurity reasons. The magnetically encoded information stored on thecards is capable of being accidentally erased or intentionally alteredby unauthorized persons to increase the units originally contained onthe memory card.

Microcircuit cards have a memory device such as an integrated circuit orprinted circuit embedded into the card which, through suitableelectrical contacts, can be connected to an external reader fordetermining the remaining value of the card. Examples of suchmicrocircuit cards may be seen in U.S. Pat. Nos. 4,737,620 to Mollet etal. and 4,719,140 to Hara et al. Although much more resistant totampering than, magnetically readable cards, microcircuit cards have thedisadvantage of being relatively expensive. Therefore, they are not wellsuited to be used for denominations of relatively small monetary value.

Contactless cards do not have any contacts for physically makingconnection to an external reader device. Instead, contactless cardsutilize means such as inductive and/or capacitive coupling for providingan external reader device with signals indicative of the monetary valueof the card. Examples of contactless cards may be seen in U.S. Pat. No.5,272,596 to Honore et al. and Brazilian Patent Specifications PI9105585 and PI 9201380.

Typically, memory cards are intended to be used only until the prepaidmonetary value of the card has been exhausted. Once this monetary amounthas been spent by the user, the card is either recycled or thrown away.For instance, when used with public telephones, the memory card ispurchased for a predetermined monetary value which is stored in the cardand the monetary value is decremented as and when the card is used.

With all types of prepaid memory cards, the cost of the card is alimiting factor in determining the practical uses or applications forprepaid memory cards. Typically, the use of prepaid memory cards ispractical only where the total monetary value represented by the cardexceeds the cost of the card itself. Thus, if the cost of the card canbe reduced, this opens the possibility for issuing smaller denomination(lower total monetary value) cards in the many existing applicationswhere prepaid cards are presently used, and also expands the number ofpotential applications or uses where prepaid memory cards could be used.

However, manufacturers are faced with a very significant challenge inreducing manufacturing costs without undesirable sacrifice in theoverall quality, reliability and durability of the memory card. Thenature of the materials and manufacturing techniques currently beingused can result in stiff or brittle memory cards. Consequently, bendingof the memory card during typical use may cause damage to or destructionof portions of the memory card.

SUMMARY OF THE INVENTION

With the foregoing in mind, it is an object of the present invention toproduce a memory card at reduced overall cost.

It is a further object of the present invention to provide an improved,reduced cost memory card having good reliability and durability.

These and other objects, features, and advantages of the presentinvention are obtained by providing a memory card having a flexiblecomposite substrate formed from a top film, a base film, and an adhesivelayer deposited between and bonding together the base film and the topfilm. Preferably, the thickness of such composite substrate is between 9and 14 mils. A layer of metal is adhered to the exposed surface of thetop film. Preferably, the metal layer is a sputter coated nickel layerhaving a surface conductivity of about 20 ohms per square. A circuitlayer overlies the metal layer to form at least one site on the memorycard which is readable by an external reading device. In addition, aprotective layer overlies and protects the circuit layer of the memorycard. Printed indicia may also be provided on the front and/or back ofthe memory card to enhance the attractiveness of the memory card andprovides instructions for use of the memory card. Preferably, both thebase film and the top film are made from a flexible thermoplasticpolymer such as a biaxially oriented polyethylene terephthalate.Preferably, the top film is thinner than the base film. The top film hasa thickness of about 1 to 2 mils and the base film has a thickness ofabout 8 to 12 mils.

The composite laminated substrate and the selection of film thicknessprovides a memory card with excellent durability and reliability.Moreover, the card has greatly improved flexibility, enabling the memorycard to be bent almost 180° in each direction during use and/or storageby the owner, without damaging or destroying the memory. As a result,the memory card can withstand greater abuse and still perform itsintended function until its monetary value has been exhausted.

In a preferred embodiment of the invention, the circuit layer of thememory card is designed to provide for storing a predetermined number of"units" of some preassigned value, and for incrementally and permanentlydecrementing the number of units as the memory card is used and theunits of value are "spent." Preferably, the memory card has a pluralityof spaced apart sites or cells which are adapted to be read by anexternal reading device. It is desirable that each site of the circuitlayer be capable of being irreversibly converted from a first readablestate to a second readable state. This ability to irreversibly converteach site enables the memory card to be decremented as and when it isused in a secure, tamper-proof manner.

The layer of metal which is adhered to the exposed surface of the topfilm is preferably a layer of nickel having a thickness of less than 0.5microns and more desirably about 0.2 microns. It is preferable forimproved readability of the cells of the contactless memory card, thatthe nickel layer have a surface conductivity of about 20 ohms persquare. Preferably in accordance with the invention, the nickel layer isformed by sputter coating onto the top film. This technique provides avery uniform and reproducible metal coating layer which providessignificant quality advantages over other metal deposition methods.

The above described memory card is preferably manufactured by anefficient low cost method which enables the memory card to be used in awide variety of applications while maintaining its high quality. Apreferred method of manufacturing the memory card includes applying athin layer of conductive metal to one surface of a polyester film, thenlaminating the opposite surface of the film by an adhesive to a thickerpolyester film to form a flexible substrate. A circuit layer is formedon the substrate by a thin layer of conductive metal with a meltingpoint equal to tin/lead (40%/60%) alloy. The circuit layer includes aplurality of spaced apart sites or cells which are capable of being readby an external contactless reading device. A protective sealant layer isthen applied over the conductive layer to protect the credit cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a memory card in accordance with thepresent invention;

FIG. 2 is a cross-sectional view of the card taken along line 2--2 ofFIG. 1;

FIG. 3 is a cross-sectional view of the substrate used in forming thememory card shown in FIGS. 1 and 2;

FIG. 4 is a perspective view, partially in cross-section, of the memorycard illustrating how the substrate is masked and sensitized inproducing the circuit layer;

FIG. 5 is a view similar to that shown in FIG. 4 illustrating the memorycard's appearance after removal of unexposed areas from the substrate;

FIG. 6 is a view similar to that shown in FIG. 4 illustrating the memorycard's appearance after electrochemical deposition of the secondcoating;

FIG. 7 is a view similar to that shown in FIG. 6 illustrating the memorycard's appearance after removal of exposed areas from the film; and

FIG. 8 is a flow diagram illustrating the method steps used tomanufacture the substrate of the memory card in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as being limited to thespecific embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout.

According to the illustrated embodiment, a flexible contactless memorycard 10 is provided for use with a reader device similar to thatdisclosed in Brazilian Patent Specification No. PI 9201380, which isincorporated herein by reference. As shown in FIG. 1, the memory card 10is of a generally rectangular configuration with rounded corners. Thememory card 10 has an overall dimension of approximately 8.5 cm (3.5inches) by 5.25 cm (2.25 inches) and a thickness of approximately 12 to16 mils. The front and/or back surface of the memory card 10 may bearprinted indicia in the form of text and/or designs as indicated at 11.

As shown best in FIG. 2, the memory card 10 is formed from a substrate12, which includes a base film 14 and a top film 16 laminated togetherby an adhesive layer 18. A thin layer 20 of a relatively high magneticconductive metal, preferably nickel, is applied to the exposed surfaceof the top film 16. A layer 22 of a lower melting point metal, such astin/lead, is then applied to the nickel layer 20. The tin/lead layerforms a circuit layer as described in more detail below. A protectivelayer 24 overlies and protects the tin/lead layer 22 and provides anabrasion resistant front surface for the card. The protective layer maybe formed of a suitable composition, such as an epoxy resin. Theprotective layer 24 may also bear printed (offset/litho) indicia 11,shown in FIG. 1, to enhance the attractiveness of the memory card 10 andprovide necessary instructions for its use.

The base film 14 and the top film 16, of this embodiment are made from adurable, flexible polymer film. Particularly suitable for use in formingthe substrate are polyester films, a commercially available example suchas PACUR from Rexham Industries Corp. The base film 14 preferably has athickness of about 10 mils. The top film 16 preferably has a thicknessof only about 2 mils.

The substrate 12 may be produced in the manner schematically shown inFIG. 8. A nickel layer 20 is deposited on one surface of the top film 16by sputter coating. The sputter coated nickel layer 20 is preferablyless than 1.0 microns in thickness, most desirably about 0.2 micronsthick to provide a surface resistivity of about 20 ohms per square. Thebase film 14 and the top film 16 are then adhesively bonded together toform a composite structure. A suitable adhesive, such as a solvent-basedpolyurethane adhesive, is applied to the surface of the top film 16opposite the nickel layer 20, or to one surface of the base film 14, orto both the top film and the base film. The adhesive-coated films arecombined in a laminator, where heat and pressure is applied to cause theadhesive to firmly bond the film layers together. The resultant laminatesubstrate 12 is collected on a reel, and subsequently cut into sheets. Across-section of the substrate 12 is best shown in FIG. 3.

FIGS. 4-7 illustrate one suitable method for making the circuit layer23, as described in Brazilian Patent Specification No. PI 9,201,380. Asshown in FIG. 4, a photosensitive layer 26 is applied to the nickellayer 20. A negative film or mask 28 containing transparent regions 30aand 30b of a predetermined desired pattern is then positioned over thephotosensitive film 26 and the assembly is exposed to ultraviolet lightto cause the photosensitive layer 26 to polymerize in the regionsexposed to ultraviolet light through the transparent regions 30a and 30bof mask 28. The nonpolymerized regions of the photosensitive layer 26are then developed, resulting in the structure shown in FIG. 5. Theremaining polymerized regions form islands 32a and 32b which adhere tothe nickel layer 22.

As shown in FIG. 6, a layer 22 of tin/lead is applied to the nickellayer 20, with the island regions 32a and 32b acting as masks preventingthe tin/lead layer from adhering in those regions. In this embodiment,the tin/lead layer 22 is applied by an electrochemical bath wherein thememory card is the cathode and the electrolyte is the anode. In thisinstance, the electrolyte is a tin/lead salt solution in a ratio ofapproximately 60% tin and 40% lead so that the deposited tin/lead layer22 has an almost eutectic composition. A low intensity current, in therange of 1 to 1.5 amperes per square decimeter is used so as to depositthe tin/lead layer 22 with a thickness of about 4 to 8 microns.

After the electrolytic deposition of the tin/lead layer 22, the islandregions 32a and 32b are removed by chemical stripping solution means toexpose areas 36a and 36b as shown in FIG. 7. The resulting structureforms a readable cell or site 40 with a fusible link 38. Although onlyone such cell 40 is shown, it will be understood that the card will havea plurality of such cells, typically and precisely arranged in columnsand rows. A protective layer 24 is then applied so as to overlie andseal the circuit layer. As shown in FIG. 1, the protective layer 24includes printed indicia 11 which is applied by suitable printingtechniques, such as offset printing or silk screen printing, to thefront surface of the protective layer 24 and optionally also to theexposed surface of the base film 14. The individual memory cards 10 arethen cut to the ISO standard shape and tested.

It is to be understood that the nickel layer 20 may be made fromconductive materials other than nickel, for instance, conductivepolymers may be used in the substrate. In addition, another conductivematerial may be substituted for the tin/lead in layer 22 so long as thedifferences in conductivity and melting points between the first andsecond layers are maintained.

The memory card 10, manufactured by the above-described method, isinserted into an external inductive reader device, such as thatdescribed in Brazilian Patent Specification No. PI 9210380, whichlocates the respective cells 40 in the card. The cells are initially ina first, non-decremented state in which the fusible link 38 is intact.In order to decrement the card by one unit of value, the fusible link 38can be fused and broken. The reader device accomplishes this by inducinga current into the cell 40, which concentrates at the fusible link 38,causing the link to melt. The cell 40 is thus irreversibly converted toa second readable state.

The reader device can detect the difference between a cell 40 in thefirst readable state and one in the second readable state. In thismanner, the reader device can determine the number of cells in the firstreadable state, to thus ascertain the number of monetary units of valueremaining on the card. When a monetary unit of value is "spent", thereader device causes a cell to be converted to the second readable stateby fusing the fusible link. The memory card 10 is usable until all itscells have been decremented in the above-described fashion.

Many modifications and other embodiments of the invention will come tomind in one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed.Although specific terms are employed, they are used in a generic anddescriptive sense only and not for purposes of limitation, and thatmodifications and embodiments are intended to be included within thescope of the appended claims.

That which is claimed:
 1. A memory card comprising:a flexible compositesubstrate having a thickness of approximately 9 to 14 mils, saidcomposite substrate comprising a flexible thermoplastic polymer basefilm, a flexible thermoplastic polymer top film laminated one surface ofsaid base film, and an adhesive layer disposed between and bondingtogether said base film and said top film, a layer of a magnetic metaladhered to the exposed surface of said top film, a circuit layeroverlying said metal layer and forming at least one site on the cardwhich is readable by an external reading device, and a protective layeroverlying and protecting said circuit layer.
 2. A card as set forth inclaim 1 additionally including a layer of printing visible on the frontof the card.
 3. A card as set forth in claim 1 wherein said base filmand said top film each comprise a polyester film, and said base film isthicker than said top film.
 4. A card as set forth in claim 3 whereinsaid top film is a biaxially oriented polyethylene terephthalate filmhaving a thickness of about 1 to 2 mils.
 5. A card as set forth in claim4 wherein said base film is a biaxially oriented polyethyleneterephthalate film having a thickness of about 8 to 12 mils.
 6. A cardas set forth in claim 1 wherein said metal layer is a layer of nickelless than 0.5 microns in thickness.
 7. A card as set forth in claim 1wherein said metal layer is a sputter coated nickel layer having asurface conductivity of about 20 ohms per square.
 8. A card as set forthin claim 1 wherein said circuit layer comprises a plurality of spacedapart sites adapted to be read by an external reading device, each siteincluding means capable of being irreversibly converted from a firstreadable state to a second readable state.
 9. A memory card comprising:aflexible composite substrate having a thickness of approximately 9 to 14mils, said composite substrate comprising a flexible polyester basefilm, a flexible polyester top film laminated to one surface of saidbase film, said top film having a thickness of about 1 to 2 mils, anadhesive disposed between and bonding together said base film and saidtop film, a layer of metal having a thickness of less than 0.5 micronadhered to the exposed surface of said top film, a circuit layeroverlying said metal layer, said circuit layer including a plurality ofspaced apart sites adapted to be read by an external reading device,each site including means capable of being irreversibly converted from afirst readable state to a second readable state, and a protective layeroverlying said circuit layer and visible on the front of the card.
 10. Acard as set forth in claim 9 wherein said base film is a biaxiallyoriented polyethylene terephthalate film.
 11. A card as set forth inclaim 9 wherein said metal layer is a layer of nickel about 0.2 micronsin thickness.
 12. A card as set forth in claim 9 wherein said metallayer is a sputter coated nickel layer having a surface conductivity ofabout 20 ohms per square.
 13. A card as set forth in claim 9 whereinsaid circuit layer comprises a plurality of spaced apart sites adaptedto be read by an external reading device, each site including meanscapable of being irreversibly converted from a first readable state to asecond readable state.
 14. A memory card comprising:a flexible compositesubstrate having a thickness of approximately 12 mils, said compositesubstrate comprising a flexible base film formed of a biaxially orientedpolyethylene film, a flexible thermoplastic polymer top film laminatedto one surface of said base film, said top film comprising a biaxiallyoriented polyethylene terephthalate film having a thickness of about 1to 2 mils, a polyurethane adhesive disposed between and bonding togethersaid base film and said top film, a layer of sputter coated nickelhaving a thickness of less than 0.5 micron adhered to the exposedsurface of said top film, a circuit layer overlying said nickel layer,said circuit layer including a plurality of inductive current measurablesites at spaced locations on the card, each site including a fusiblelink which can be irreversibly broken by application of an electricalcurrent of sufficient magnitude to convert the site from a first stateto a second state which can be read from the card by an external reader,and a protective layer overlying and protecting said circuit layer, saidprotective layer including printed indicia visible on the front of thecard.
 15. A flexible plastic substrate for forming a memory card, saidsubstrate comprising a flexible base film formed from a biaxiallyoriented polyethylene film, a flexible thermoplastic polymer top filmlaminated to one surface of said base film, said top film comprising abiaxially oriented polyethylene terephthalate film having a thickness ofabout 1 to 2 mils, a polyurethane adhesive disposed between and bondingtogether said base film and said top film, and a layer of sputter coatednickel having a thickness of less than 0.5 micron adhered to the exposedsurface of said top film.
 16. A substrate as set forth in claim 15wherein said substrate has a thickness of approximately 12 mils.
 17. Amethod of forming a memory card comprising:applying a thin layer of ametal to one surface of a polyester film; laminating the oppositesurface of said film to a thicker polyester film; forming a circuitlayer on said thin layer of conductive metal; and applying a protectivelayer over said circuit layer.
 18. A method according to claim 17wherein said step of applying a thin layer of a conductive metal to onesurface of a polyester film comprises sputter coating a thin layer ofnickel onto one surface of a polyester film of 1 to 2 mils thickness,and said step of laminating comprises laminating said opposite surfaceof said film to a thicker polyester film using a polyurethane adhesive.19. A method of forming a memory card comprising sputter coating a layerof nickel of less than 0.5 micron onto one surface of a biaxiallyoriented polyethylene film of 1 to 2 mils thickness;laminating theopposite surface of said film to a biaxially oriented polyethyleneterephthalate film of 8 to 12 mils thickness; forming on said thin layerof conductive metal a plurality of spaced apart sites adapted to be readby an external reading device, each site including means capable ofbeing irreversibly converted from a first readable state to a secondreadable state; and applying a protective layer over said conductivelayer.